The field of the present invention is drive mechanisms for timing control valves in two-cycle engines.
Two-cycle engines typically include ports through the cylinder wall for intake, scavenging and exhaust. Such openings are repeatedly opened and closed by the piston during operation of the engine. In the case of the exhaust porting, the upper edge of the exhaust port determines the timing for both the opening and closing of the port by the piston.
Typically the power of two-cycle engines is affected by the timing of the exhaust port such that engines are tuned for power in a specific engine speed range. Such two-cycle engines may be tuned for power at low engine speeds where the use is typically for low speed driving. Tuning for power at high engine speeds may also be employed for other specific uses. However, in both instances, the range of engine speeds providing reasonable engine power are limited.
To at least partially overcome this difficulty with two-cycle engines, devices have been employed which alter the upper edge of the exhaust port. Such devices are typically incorporated in or in conjunction with the exhaust passage of the engine. Valves extend to the upper port area where they may define an upper edge of the exhaust port below the actual upper edge of the port opening. By controlling the location of such valve members, the timing may be varied in accordance with changes in engine speed.
One difficulty previously encountered with such timing devices is that they operate at fixed speeds. Consequently, they may either move too abruptly or too slowly depending on the rate of change of engine speed. As a consequence, the engine output may be adversely affected.